Polyethylene terephthalate is used as a raw material for containers for juice, refreshing drink, carbonate drink, seasoning, detergent, cosmetic and the like, since it is excellent in mechanical strength, heat resistance, transparency and gas-barrier properties, as compared with other plastic materials. In some applications, however, it has such problems that it cannot be filled or fully sterilized at high temperatures due to the lack of sufficient resistance to high heat, that it shows low efficiency because of its low alkali washing temperature for recycling use, and that the amount of the content decreases due to its insufficient gas-barrier properties. Therefore, the development of polyethylene terephthalate having excellent heat resistance and high gas-barrier properties has been strongly desired.
Polyethylene-2,6-naphthalene dicarboxylate (to be abbreviated as PEN hereinafter) is widely used as a raw material for magnetic films, drink bottles, packing materials and a variety of moldings. However, since a conventional resin containing a naphthalene ring such as PEN has a low crystallization speed, it is desired to improve crystallization speed for the acceleration of its molding cycle and to rise crystallinity for the improvement of its dimensional stability, chemical resistance and heat resistance. As solutions for these problems, there have been proposed many methods including one which uses a high-temperature mold and one in which a crystal nucleating agent or crystallization promoting agent is added.
Japanese Laid-Open Patent Application 51-143060 discloses a polyether imide/polyester mixture containing a polyether imide represented by the following formula (A): ##STR1## wherein a is a number larger than 1, Z is an o-phenylene group, p-phenylene group or aromatic group having up to 17 carbon atoms, and R is a divalent organic group such as an aromatic hydrocarbon having 6 to 20 carbon atoms,
and a polyester represented by the following formula (B): ##STR2## wherein b is a number larger than 1, R' is an alkylene group having 1 to 10 carbon atoms, and two carbonyl groups are at the meta- or para-position.
This mixture exhibits a lower melt viscosity than that of the polyether imide.
Japanese Laid-Open Patent Application 59-37161 discloses a heat resistant polyester container made of an unoriented amorphous sheet formed from a resin composition comprising 60 to 99 wt % of a polyethylene terephthalate and 40 to 1 wt % of a polyether imide. This publication discloses the same polyether imide as that represented by the above formula (A) disclosed by the above Japanese Laid-Open Patent Application 51-143060.
Japanese Laid-Open Patent Application 6-49206 discloses a polyimide comprising 3,3',4,4'-benzophenone tetracarboxylic dianhydride as a monomer unit and 1,4-diaminobutane as a monomer unit and a polymer blend of the polyimide and a thermoplastic polymer including polyethylene terephthalate or polybutylene terephthalate. Example III shows that the melting point of a polyimide obtained from 3,3',4,4'-benzophenone tetracarboxylic anhydride and diamine consisting of 75% of 1,4-diaminobutane and 25% of 3,3-oxydianiline could not be detected, while polyimides in other examples are crystalline polyimides having a melting point.
On pages 677 and 678 of Research Disclosure November 1987 and pages 1453 to 1458 of ANTEC' 95 is disclosed a blend of a polyether imide (ULTEM1000 of GE Corp.) comprising recurring units represented by the following formula and polyethylene-2,6-naphthalene dicarboxylate (PEN). ##STR3##
Although the glass transition temperature of this blend is improved due to the high glass transition temperature of the ULTEM1000, it is difficult to mold the blend due to its increased melt viscosity. In addition, the obtained molded article is fragile, and its delamination which occurs when a film is bent to undergo stress is not improved.
Japanese Laid-Open Patent Application 7-228761 discloses a polyester resin composition comprising a copolyester consisting of ethylene terephthalate units and ethylene naphthalate units and the polyether imide substantially same as that represented by the above formula (A). The publication also discloses that this resin composition is used in exterior trim parts such as auto parts, or in housings for office equipment, or the like.
U.S. Pat. No. 5,057,595 discloses a composition comprising a copolyester comprising 4,4'-biphenyldicarboxylic acid as an acid component and 1,4-cyclohexane dimethanol and ethylene glycol as glycol components and a modifier such as a composition containing ULTEM of GE Corp.
U.S. Pat. No. 5,037,946 discloses a composition comprising a copolyester comprising 4,4'-biphenyldicarboxylic acid as an acid component and 1,6-hexanediol and ethylene glycol as glycol components and the same modifier as described above.